Category: Haskell

If you like a tool, never look at its headers.

Following hot on the heels of this astonishing header from Boost, here are some excerpts from the module defining tuples in the Glasgow Haskell Compiler 7.4.1:

data (,) a b = (,) a b
    deriving Generic
data (,,) a b c = (,,) a b c
    deriving Generic

(If you can’t read Haskell: (,) a b is another notation for (a, b). This defines types for two- and three-element tuples, with a default implementation of the Generic interface.) Okay so far? The file proceeds to define 4-tuples, 5-tuples, and so on until we get to the 8-tuple definition:

data (,,,,,,,) a b c d e f g h = (,,,,,,,) a b c d e f g h
    -- deriving Generic

Surprise commented-out deriving clause! But it’s all plain sailing from here… until we get to 63-tuples:

data (,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,) a b c d e f g h i j k l m n o p q r s t u v w x y z a_ b_ c_ d_ e_ f_ g_ h_ i_ j_ k_ l_ m_ n_ o_ p_ q_ r_ s_ t_ u_ v_ w_ x_ y_ z_ a__ b__ c__ d__ e__ f__ g__ h__ i__ j__
 = (,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,) a b c d e f g h i j k l m n o p q r s t u v w x y z a_ b_ c_ d_ e_ f_ g_ h_ i_ j_ k_ l_ m_ n_ o_ p_ q_ r_ s_ t_ u_ v_ w_ x_ y_ z_ a__ b__ c__ d__ e__ f__ g__ h__ i__ j__
    -- deriving Generic
{- Manuel says: Including one more declaration gives a segmentation fault.
data (,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,) a b c d e f g h i j k l m n o p q r s t u v w x y z a_ b_ c_ d_ e_ f_ g_ h_ i_ j_ k_ l_ m_ n_ o_ p_ q_ r_ s_ t_ u_ v_ w_ x_ y_ z_ a__ b__ c__ d__ e__ f__ g__ h__ i__ j__ k__
 = (,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,) a b c d e f g h i j k l m n o p q r s t u v w x y z a_ b_ c_ d_ e_ f_ g_ h_ i_ j_ k_ l_ m_ n_ o_ p_ q_ r_ s_ t_ u_ v_ w_ x_ y_ z_ a__ b__ c__ d__ e__ f__ g__ h__ i__ j__ k__

…followed by commented-out definitions of everything up to 100-tuples.

Yesod web application dependencies

I have been experimenting with using Yesod to throw together a web application or two. My experience so far has been broadly positive—if you like computers to check things for you, I recommend it. ((assuming you like deciphering compiler error messages when the computer says no, that is)) That said, watching the full chain of dependencies fly past was moderately entertaining: ((for a quiet Wednesday morning…))

parsec-3.1.2

An excellent parser-combinator library, widely imitated. This wouldn’t be funny, except…

attoparsec-0.10.1.0

Another excellent parser-combinator library, inspired by parsec.

base-unicode-symbols-0.2.2.3

This defines a bunch of Unicode aliases for standard functions with boring ASCII names. Why write:

x `elem` xs

when you could write:

x ∈ xs

Invaluable!

utf8-light-0.4.0.1 and utf8-string-0.3.7

Two UTF-8 encoding libraries!

semigroups-0.8

“In mathematics, a semigroup is an algebraic structure consisting of a set together with an associative binary operation. A semigroup generalizes a monoid in that there might not exist an identity element. It also (originally) generalized a group (a monoid with all inverses) to a type where every element did not have to have an inverse, thus the name semigroup.”